Dummett was handed his fifth international cap by manager Ryan Giggs, playing for 61 minutes at Wrexham's Racecourse Ground as Ben Woodburn netted a stoppage-time winner for the Dragons.
Wales kick off their Euro 2020 qualification campaign against Slovakia on Sunday, with the possibility of Dummett coming face to face with Newcastle team-mate Martin Dúbravka at the Cardiff City Stadium.
Elsewhere, Newcastle under-23 centre-back Oisin McEntee played the full 90 minutes in Republic of Ireland under-19s' 5-0 thrashing of Romania in their European Championship Elite Round Qualifiers.
The Irish, currently chasing the one automatic qualifying spot for this summer's finals in Armenia, were too strong for their opponents in Krasnodar.